>On Thu, May 04, 2000 at 11:58:29PM -0000, Eric Smith wrote:
>> The problem with direct CD to CD-R copy is that the OS, device driver,
>> and even the CD-ROM drive do not have any reliable way to know how many
>> sectors there are on the source disc, unless they can rely on file
>> system data, i.e., the ISO 9660 header. If the disc isn't 9660, you'd
>> need some other way to tell.
>FWIW, my Panasonic CW-7502 CD-R drive gives a correct size in response to
>a SCSI "READ CAPACITY" command. Are you saying that most drives don't
>support this?
The drive supports it, but the OS may not. For instance, whenever I want
to image a CD under Linux, I dd if=/dev/cdrom of=wherever.dsk bs=2048, and
it always ends with an error after it runs past the end of the disk. (And
there are errors logged to the console, too, showing that it failed
trying to read the nonexistent sector numbers.) Happens with several different
CD-ROM and CD-R drives, all of which *do* report actual device sizes
correctly.
Of course, if you bypass the stupid Linux device driver that doesn't know
any better and bang on the CD directly, you may not have that problem. Or
if you switch to a real OS.
This is RedHat 6.0 and 6.1, with various Adaptec SCSI host adapters and
the "stock" Linux drivers. Maybe you have a NCR-based host adapter and
the drivers there are smart enough not to run off the end?
--
Tim Shoppa Email: shoppa_at_trailing-edge.com
Trailing Edge Technology WWW: http://www.trailing-edge.com/
7328 Bradley Blvd Voice: 301-767-5917
Bethesda, MD, USA 20817 Fax: 301-767-5927
Received on Thu May 04 2000 - 20:59:28 BST